1. Field of the Invention
The invention relates generally to GNSS/INS systems, and more particularly, to a system and method for calculating lever arm values for the GNSS/INS systems.
2. Background Information
Global navigation satellite system (GNSS) and inertial navigation system (INS) integration is nowadays a standard approach for certain navigation and remote sensing applications that utilize position, velocity, and/or orientation information. To compensate for sensor drifts in the INS, the INS may be periodically provided with position and velocity information from an associated GNSS receiver. The INS uses the information from the GNSS receiver to accurately compute updated position, velocity, and/or orientation utilizing information from its sensors.
The INS sensors are integrated into an inertial measurement unit (IMU). The IMU is not typically mounted at the same location as a GNSS antenna that operates with the GNSS receiver. For example, the GNSS antenna is usually mounted on the outside of a vehicle, such as on the roof, for a sky view, while the IMU may be mounted on the inside of the vehicle. Accordingly, the INS and GNSS components of the integrated system have different measurement reference points. The reference point of the GNSS component is the location of the GNSS antenna, and the reference point of the INS component is a selected location with reference to the IMU.
A 3-dimensional vector between the respective reference point of the INS component and the GNSS component is known as a “lever arm,” and the lengths of the vector in the x, y, and z dimensions are referred to as “lever arm values.” The INS utilizes the lever arm values to combine information received from the GNSS receiver with the information read from the sensors of the INS. Thus, accurate lever arm values are crucial for the integrated GNSS/INS system to accurately compute position, velocity, and/or orientation information.
Currently, users may utilize a theodolite to very precisely derive the lever arm values. However, setting up an associated network to make the necessary measurements may be daunting and also extremely expensive, and thus, prohibitive to many users. A common alternative is for a user to measure the lever arm values using a plumb bob and tape measure. However, utilizing the plumb bob and tape measure is tedious and also highly susceptible to user error. Thus, what is needed is an easy, accurate, and relatively inexpensive technique for calculating the lever arm values.